Material handling device with inflatable air pads

ABSTRACT

An air film pallet with a plurality of inflatable air pads connectable to a source of pressurized air through separate sonic flow restrictors. Each pad is connected to a separate air chamber through a separate flow restrictor located downstream of the associated sonic flow restrictor so that vertical oscillation is prevented.

United States Patent Inventor Appl. No

Filed Patented Assignee Elgin S. Williams Athens, Mich.

Jan. l2, I970 Aug. 10, 1971 Clark Equipment Company MATERIAL HANDLING DEVICE WITH INI'LATAILEAIRPADS 4Clalms,3llrawingllgs.

u.s.c1. 180/121, l80lll8,l80/l24 1.1.121. 360111/00 FieldoISeu-d 180/121, I l24,l25,ll8

[56] References Cited I UNITED STATES PATENTS 3,25 1,432 5/1966 Fischer et a1. 180/124 3,318,406 5/1967 Scheel 180/ 1 24 X 3,340,943 9/1967 Hirsch 180/1 18 3,392,800 7/1968 Swamy 180/125 3,513,936 5/1970 Crowley et al 180/124 Primary Examiner-A. Harry Levy Anomeys- Kenneth C. Witt, John C. Wiessler, Robert H.

Johnson and Reginald J. Falkowski ABS'IRACT: An air film pallet with a plurality of inflatable air pads connectable to a source of pressurized air through separate sonic flow restrictors. Each pad is connected to a separate air chamber through a separate flow restrictor located downstream of the associated sonic flow restrictor so that vertical oscillation is prevented.

PATENTEU AUGIOIHYI 3 599 19 FIG. I

I N V/if-J'l (J/4 ELGIN S. WILLIAMS ATTORNEY MATERIAL HANDLING DEVICE WITH INFLATABLE AIR PADS BACKGROUND OF THE INVENTION The field of art to which this invention relates includes motor vehicles with fluid pads, and more specifically inflatable fluid pads.

Material-handling devices which utilize inflatable air pads frequently are troubled with undesirable self-sustaining vertical oscillations which vary, depending upon floor surface conditions, rate of airflow and loading. Once .such oscillations start, the downward motion of the device causes the restric tion to flow of air out from between the pad and floor to increase. As a result the air pressure in the pad increases, the increasing air pressure gradually stopping downward motion of the device, and then forcing the device upward. As the pad moves upward, the restriction to flow of air out from between the pad and floor decreases. As a result the air pressure in the pad decreases rapidly, and so upward movement of the device stops. The device then starts downward, thereby repeating the cycle. Apparently, the combined spring rate of the pressurized air. and the elasticity of the pad material results in a natural frequency (a fairly broad range of frequencies) of such low period that the pad becomes sufficiently overpressurized during the lower end of downward motion to literally throw the device upward.

Therefore, it is a principal object of my invention to dampen vertical oscillations in a material handling device utilizing inflatable air pads.

SUMMARY or THE INVENTION In carrying out my invention in a preferred embodiment, I provide a load-engaging member. Mounted to the load-engaging member is at least one inflatable air pad and at least one air chamber. The air pad is connectable, through a sonic flow restrictor, to a source of pressurized air and the air chamber is connected, through another flow restrictor, to the air pad downstream of the sonic flow restrictor.

The above and other objects, features, and advantages of my invention will be more readily apparent to persons skilled in the art whenthe detailed description is considered in conjunction with the drawing.

'BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially schematic. cross section of a pallet utilizing may invention,

FIG. 2 is a partially schematic bottom view of the pallet of FIG. 1 with bottom plate 26 removed, and

FIG. 3 is a schematic diagram showing pad 14 in cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, the reference numeral denotes generally a material-handling device having a load-supporting member or platform 12 to the underside of which a plurality of inflatable air pads l4, l6, l8 and are attached.

Platform 12 includes a generally square hollow frame 22 to which a top plate 24 and a bottom plate 26 are attached. The air pads are mounted on the underside of bottom plate 26. Further, frame 22 is divided into a plurality of air chambers or fluidic capacitors 28, 30, 32 and 34.

Device 10 includes a main air supply conduit 36 having an inlet 38 which is connectuble to a source of pressurized air or other suitable fluid by means of a flexible hose 40. Branch conduits 42, 44, 46 and 48 connect supply conduit 36 with pads l4, l6, l8 and 20, respectively, so that pressurized air can be supplied to the various pads from conduit 36.

Disposed in branch conduit 42 is a sonic flow restrictor 50. Similarly, sonic flow restrictors 52, 54 and 56 are disposed in branch conduits 44, 46 and 48, respectively. By sonic flow restrictor I mean a device that restricts flow through conduit such that for the pressure differential involved the maximum possible flow of fluid is passing through the restriction at sonic speed. Thus, variations in pressure of the fluid downstream of the sonic flow restrictor have no effect upon the flow of fluid through the restrictor so long as the maximum pressure downstream is below the critical differential for maintaining sonic flow through the restrictor. The importance of this is that the pressure within air pads 14, 16,18 and 20 can vary, within limits, and the flow of pressurized air to each pad from supply conduit 36 will remain constant. This is advantageous because even if the load carried by device 12 is otfcenter the airflow to all of the pads will remain constant and the air pressure in the pads carrying a greater proportion of the load will increase in order to offset the additional weight that must be supported by these pads. The result is a very stable device even when offcenter loads are being carried.

Pad 14 is in communication with air chamber 28 by means of a conduit 58 connected to branch conduit 42 to downstream of sonic flow restrictor 50. In a similar manner air pads l6, l8 and 20 are connected to air chambers 30, 32 and 34, respectively, by conduits 60, 62 and 64. Disposed in conduit 58 is a flow restrictor 66. Likewise flow restrictors 68, 70 and 72 are disposed in conduits 60, 62 and 64, respectively. Air chambers 28, 30, 32 and. 34 together with flow restrictors 66, 68, 70 and 72 serve to dampen vertical oscillation of device 10 as will be explained in more detail shortly. Incidentally, while only a single air pad is shown connected to each air chamber, in'some circumstances it is possibleto'connect two or more air pads to a givenair chamber in'order to dampen vertical oscillation.

Referring now specifically to FIG. 3, some of the details of air pad 14 will be described. It' is felt to be necessary to describe in detail only a single one of the air pads since they are all identical. Air pad 14 includes a backing plate 74 to which flexible diaphragm 76 is connected at the periphery and center thereof to form an annular inflatable air chamber 78. Located in diaphragm 76 is a pluralityof openings 80 which serve to communication air chamber' 78 with a plenum chamber 82 formed by air pad 14 and the surface 84 over which it is operating. Briefly, the operation of air pad 14 is such that when pressurized air is supplied to chamber 78 the pad inflates, forming plenum chamber 82 with the surface 84 over which the pad is operating. Pressurized air flows. out of chamber 78 through openings 80 and intov plenum chamber 82. Pressurized air flows from plenum chamber 82 out from under pad 14, thereby providing'an air film of approximately 0.015 of an inch thickness between air pad 14 and the supporting surface, thereby greatly reducing thefriction between the pad and supporting surface so that the pad may be readily slid along the surface.

Referring again to pad 14, by way of example, the pressure in chamber 78 will be determined by that proportion of the total load that pad 14 is carrying. Now, should platform 12 have an additional downward force directed to it causing it to move downward so that the throttling effect on the air escaping out from under pad 14 will be increased, the pressure in chamber 78 will increase. The increasing pressure in chamber 78, as pointed out above, will stop downward movement of pad 14. However, if the combined spring rate of the pressurized air and the elasticity of the diaphragm material results in a natural frequency of such low period that the diaphragm becomes overprcssurized, the portion of platform [2 overlying air pad l4 will laterally be thrown upward. As the device moves upward the throttling effect between pad l4 and the supporting surface becomes less, thus allowing the air to escape out from under pad 14 faster with the result that there is a rapid drop of pressure in chamber 78. Consequently, a self-sustaining vertical oscillation tends to be set up, but is prevented from being set up by air chamber 28 and flow restrictor 66 which serve to dampen out any vertical oscillatory motion that is started in pad 14.

other pads are identical in construction and operation, and so such explanation applies equally to the other pads.

At this point it will be apparent that my invention provides a device having inflatable air pads which is stable under offcenter loading and in which vertical oscillations are dampened.

While I have described in detail only a single preferred embodiment of my invention, it will be understood that this description is intended to be illustrative only and that my invention is subject to various changes and modifications which do not depart from the scope and spirit of it. For example, the material-handling device may incorporate any number of air pads. Therefore, the limits of my invention should be determined from the following appended claims.

lclaim:

l. A material-handling device comprising a load supporting member, an inflatable fluid pad mounted on said member, a fluidic capacitor mounted on said member, conduit means connected to said pad and connectable to a source of pressurized fluid, said conduit means including sonic flow restriction means and second flow restriction means connecting said capacitor to said pad downstream of said sonic flow restriction means.

2. For use with a source of pressurized fluid, a material-handling device comprising a frame, said frame being divided into a plurality of fluid chambers, a plurality ofinflatable fluid pads connected to said frame, conduit means connected to each pad, said conduit mans including an inlet connectable to the source of pressurized fluid and a plurality of sonic flow restrictors, each sonic flow restrictor being disposed between a different one of said pads and said inlet, and a plurality of second flow restrictors, each one of said second flow restrictors being connected between one of said chambers and one of said pads downstream of the associated sonic flow restrictor.

3. For use with a source of pressurized air, a material-handling device comprising a load-supporting member, said member including a frame, said frame being divided into a plurality of air chambers, a plurality of inflatable air pads mounted on said member, conduit means connected to each one of said pads, said conduit means including an inlet connectable to the source of pressurized fluid, a plurality of sonic flow restrictors disposed in said conduit means, each sonic flow restrictor being located between a different one of said pads and said inlet, and a plurality of second flow restrictors, each one of said second flow restrictors being connected between one of said chambers and one of said pads downstream of the associated sonic flow restrictor.

4. The device as set forth in claim 3 wherein said chambers have fixed volumes. 

1. A material-handling device comprising a load supporting member, an inflatable fluid pad mounted on said member, a fluidic capacitor mounted on said member, conduit means connected to said pad and connectable to a source of pressurized fluid, said conduit means including sonic flow restriction means and second flow restriction means connecting said capacitor to said pad downstream of said sonic flow restriction means.
 2. For use with a source of pressurized fluid, a material-handling device comprising a frame, said frame being divided into a plurality of fluid chambers, a plurality of inflatable fluid pads connected to said frame, conduit means connected to each pad, said conduit means including an inlet connectable to the source of pressurized fluid and a plurality of sonic flow restrictors, each sonic flow restrictor being disposed between a different one of said pads and said inlet, and a plurality of second flow restrictors, each one of said second flow restrictors being connected between one of said chambers and one of said pads downstream of the associated sonic flow restrictor.
 3. For use with a source of pressurized air, a material-handling device comprising a load-supporting member, said member including a frame, said frame being divided into a plurality of air chambers, a plurality of inflatable air pads mounted on said member, conduit means connected to each one of said pads, said conduit means including an inlet connectable to the source of pressurized fluid, a plurality of sonic flow restrictors disposed in said conduit means, each sonic flow restrictor being located between a different one of said pads and said inlet, and a plurality of second flow restrictors, each one of said second flow restrictors being connected between one of said chambers and one of said pads downstream of the associated sonic flow restrictor.
 4. The device as set forth in claim 3 wherein said chambers have fixed volumes. 